1. Field of the Invention
This invention relates to data storage systems and more particularly to a system and method for on-line replacement of an existing data storage subsystem.
2. Description of Related Art
Data processing centers of businesses and organizations such as banks, airlines and insurance companies, for example, rely almost exclusively on their ability to access and process large amounts of data stored on a data storage device. Data and other information which is typically stored on one or more data storage devices which form part of a larger data storage system is commonly referred to as a database.
Databases are nearly always xe2x80x9copenxe2x80x9d and constantly xe2x80x9cin usexe2x80x9d and being accessed by a coupled data processing system, central processing unit (CPU) or host mainframe computer. The inability to access data is disastrous if not a crisis for such business and organizations and will typically result in the business or organization being forced to temporarily cease operation.
During the course of normal operations, these businesses and organizations must upgrade their data storage devices and data storage systems. Although such upgrading sometimes includes only the addition of data storage capacity to their existing physical systems, more often than not upgrading requires the addition of a completely separate and new data storage system. In such cases, the existing data on the existing data storage system or device must be backed up on a separate device such as a tape drive, the new system installed and connected to the data processing unit, and the data copied from the back-up device to the new data storage system. Such activity typically takes at least two days to accomplish. If the conversion takes more than two days or if the business or organization cannot withstand two days of inoperability, the need and desire to upgrade their data storage system may oppose an insurmountable problem.
Some prior art data copying methods and systems have proposed allowing two data storage systems of the same type, a first system and a second system, to be coupled to one another, and allowing the data storage systems themselves to control data copying from the first to the second system without intervention from or interference with the host data processing system. See for example, the data storage system described in U.S. patent application Ser. No. 08/052,039 (now U.S. Pat. No. 5,544,347) entitled REMOTE DATA MIRRORING, fully incorporated herein by reference, which describes one such remote data copying facility feature which can be implemented on a Symmetrix 5500 data storage system available from EMC Corporation, Hopkinton, Mass.
Although such a system and method for data copying is possible, in most instances, the first and second data storage systems are not of the same type, or of a type which allow such a xe2x80x9cbackgroundxe2x80x9d data migration to take place between the two data storage systems, unassisted by the host and while the database is open. Additionally, even on such prior art data storage systems, migrating data as a xe2x80x9cbackgroundxe2x80x9d task while the database is xe2x80x9copenxe2x80x9d does not take into account the fact that the data is constantly changing as it is accessed by the host or central processing unit and accordingly, if the old system is left connected to the host, there will always be a disparity between the data which is stored on the old data storage system and the data which has been migrated onto the new data storage system. In such cases, the new data storage system may never fully xe2x80x9ccatch upxe2x80x9d and be able to be completely synchronized to the old data storage system.
Accordingly, what is needed is a system and method for allowing data migration between a first data storage system and a second data storage system while the database is open and in real-time, completely transparent to the host or data processing unit with minimal interruption to interaction with the one or more host or data processing systems.
Therefore it is an object of this invention to provide a method for providing on-line, real-time, transparent data migration between two data storage devices with minimal interruption to host system operations.
In accordance with this invention, data elements migrate from an existing storage device to a replacement storage device in a data processing system with a host system having a plurality of input-output connections available to storage devices wherein data element transfers with the existing storage device occur over a first input-output connection in response to data transfer requests. The method establishes a data migration configuration concurrently with the processing of host system data transfer requests by establishing a first path between the replacement storage device and a second host system input-output connection and by establishing a second path between the existing and replacement storage devices. Data transfer requests from the host system are rerouted to the second host system input-output connection. Thereafter first data transfers between the host system and the replacement storage device occur in response to data transfer requests from the host system over the first path. Second transfers from the existing storage device to the replacement storage device occur over the second path. The first and second transfers continue until all the data elements have migrated from the existing storage device to the replacement storage device.
In accordance with another aspect of this invention, data elements migrate from an existing storage device to a replacement storage device in a data processing system with a plurality of host computers wherein each host computer has a plurality of input-output connections available to storage devices and wherein data element transfers with the existing storage device occur over a first host computer input-output connection with each of the plurality of host computers and wherein the replacement storage device has a plurality of input-output connections. As a first step the method establishes a data migration configuration concurrently with the processing of host system data transfer requests from the host computers by establishing first paths between plurality of storage device input-output connections for the replacement storage device and a second host computer input-output connection for each of the plurality of host computers, and by establishing a second path between the existing and replacement storage devices. Data transfer requests from each of the plurality of host computers are rerouted to their corresponding second host system input-output connections. Thereafter, first transfers are performed between each of the plurality of host computers and the replacement storage device in response to data transfer requests from the host computers over the first paths and second transfers are performed from the existing storage device to the replacement storage device over the second path. These transfers continue until all the data elements have migrated from the existing storage device to the replacement storage device.